You can downgrade your iPhone 4 iOS 5.0.1 to iOS 4.3.3 using the method explained below . After downgrading to iOS 4.3.3 you will be able to use the 4.3.3 untethered jailbreak using Redsnow , PwnageTool , JailbreakMe or Snowbreeze .

Note : iOS 4.3.3 SHSH Blobs required . SHSH Blobs can be saved using TinyUmbrella or iSHSHit tool available on Cydia for Free . iPhone Baseband is not downgraded during this process .